The invention relates to a device and a method for measuring an electrical current of a battery having multiple battery modules. Furthermore, the invention relates to a battery comprising such a device for measuring an electrical current.
In the case of hybrid vehicles or solely electrically driven vehicles, it is necessary to store large quantities of electrical energy. In order to store the electrical energy, battery systems are used that comprise in each case a multiplicity of battery cells and an associated battery management system. The battery management system comprises monitoring units with which the state of the battery or of the battery module and of the battery cells can be monitored, and also a battery control unit.
The monitoring units of the battery comprise monitoring sensors and direct the signals of the sensors to the battery control unit. The monitoring sensors ascertain important state parameters of the battery cells that include in particular the temperature, the voltage, the cell internal resistance and the through-flowing electrical current. In order to be able to compile with current safety regulations, the relevant monitoring sensors are generally embodied in a redundant manner.
US 2010/0271936 A1 discloses a battery module that comprises a multiplicity of battery cells. The individual battery cells of the battery module are connected to one another in the form of a series connection by way of the cell connector. The battery module comprises furthermore a cell monitoring unit in order to monitor the temperature of the battery module, the through-flowing current and also the voltages of the individual battery cells. Multiple thermistors are provided in the region of the battery cells for the purpose of monitoring the temperature. In order to measure the voltage of the battery cells, each cell connector is connected to the monitoring unit. The voltage of a battery can then be measured as the voltage between the two cell connectors that are connected to this battery cell. For the purpose of measuring the electrical voltage, a cell connector is connected to the monitoring unit by way of two lines. The first line is arranged in the region of the connection to a first battery cell and the second line is arranged in the region of the connection to a second battery cell. An electrical current that is flowing by way of the cell connection causes a voltage drop at this cell connector. This voltage drop at the cell connector can be measured using the monitoring unit by way of the two connecting lines. It is possible to conclude the magnitude of through-flowing current from this measured voltage drop together with a predetermined electrical resistance of the cell connector.
US 2011/0199091 A1 describes a current sensor for a battery. The current sensor comprises a measuring resistor, a circuitry and a housing. The current sensor is arranged on the battery in such a manner that it is integrated in the electrical current circuit between the consumer and the battery. For this purpose, it is arranged on one of the battery poles. A voltage drop occurs at the measuring resistor and is measured. An integrated circuitry evaluates the voltage difference and can broadcast the result by way of a databus by way of example a CAN bus.
A disadvantage of the prior art is that in order to comply with predetermined safety requirements, such as by way of example a specific ASIL Level (Automotive Safety Integrity Level), it is necessary to use multiple sensors to measure the battery current. The hitherto required redundancy increases the effort involved in integrating the current sensors and also the costs.